In this paper, we consider a distributed cooperative network using
STNC over independent but not necessarily identically distributed
(i.n.i.d.) Nakagami-\(m\)  fading channels, which generalizes the
result in [1]}. In this network, multiple
sources communicate with a single destination with the assistance of
multiple relays. Here, we focus on decode-and-forward (DF) protocol
at the relays, which arises from the fact that this protocol has
been successfully deployed in practical wireless standards, e.g.,
3GPP Long Term Evolution (LTE) and IEEE 802.16j WiMAX [2]}.
Different from [1]}, we examine two fundamental
questions as follows: “1) What is the impact of STNC on the
symbol error rate (SER) in general Nakagami-\(m\)  fading channels?”
and “2) Can we provide closed-form expressions for the SER in
Nakagami-\(m\)  fading to alleviate the burden of Monte Carlo
simulations?” The rationale behind these questions is that
Nakagami-\(m\)  fading covers a wide range of typical fading scenarios
in realistic wireless applications via the \(m\)  parameter. Notably,
Nakagami-\(m\)  fading encompasses Rayleigh fading (\(m = 1\) ) as a
special case [4]}. To tackle these questions, we
first derive new closed-form expressions for the exact SER, which
are valid for multiple phase shift-keying modulation (\(M\) -PSK) and
\(M\) -ary quadrature amplitude modulation (\(M\) -QAM). To further
provide valuable insights at high signal-to-noise ratios (SNRs), we
derive new compact expressions for the asymptotic SER, from which
the diversity gain is obtained. Specifically, it is demonstrated
that the diversity order is determined by the Nakagami-\(m\)  fading
parameters of all the channels, but independent of the number of
sources. Various numerical results are utilized to examine the
impact of the number of relays, relay location, Nakagami-\(m\)  fading
parameters, power allocation, and nonorthogonal codes on the SER.
Importantly, it is shown that nonorthogonal codes provide higher
throughput than orthogonal codes, while guaranteeing full diversity
over Nakagami-\(m\)  fading channels. Our analytical expressions are
substantiated via Monte Carlo simulations.
